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authorBenjamin LaHaise <bcrl@kvack.org>2009-01-10 23:00:22 -0500
committerIngo Molnar <mingo@elte.hu>2009-01-11 05:05:33 +0100
commit7106a5ab89c50c6b5aadea0850b40323804a922d (patch)
treed4ce5df5ff89da035b6dd092bbe089757def7c34 /arch/x86/include/asm/system.h
parentc59765042f53a79a7a65585042ff463b69cb248c (diff)
x86-64: remove locked instruction from switch_to()
Impact: micro-optimization The patch below removes an unnecessary locked instruction from switch_to(). TIF_FORK is only ever set in copy_thread() on initial process creation, and gets cleared during the first scheduling of the process. As such, it is safe to use an unlocked test for the flag within switch_to(). Signed-off-by: Benjamin LaHaise <bcrl@kvack.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/include/asm/system.h')
-rw-r--r--arch/x86/include/asm/system.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index 8e626ea33a1..fa47b1e6a86 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -96,15 +96,15 @@ do { \
"thread_return:\n\t" \
"movq %%gs:%P[pda_pcurrent],%%rsi\n\t" \
"movq %P[thread_info](%%rsi),%%r8\n\t" \
- LOCK_PREFIX "btr %[tif_fork],%P[ti_flags](%%r8)\n\t" \
"movq %%rax,%%rdi\n\t" \
- "jc ret_from_fork\n\t" \
+ "testl %[_tif_fork],%P[ti_flags](%%r8)\n\t" \
+ "jnz ret_from_fork\n\t" \
RESTORE_CONTEXT \
: "=a" (last) \
: [next] "S" (next), [prev] "D" (prev), \
[threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
[ti_flags] "i" (offsetof(struct thread_info, flags)), \
- [tif_fork] "i" (TIF_FORK), \
+ [_tif_fork] "i" (_TIF_FORK), \
[thread_info] "i" (offsetof(struct task_struct, stack)), \
[pda_pcurrent] "i" (offsetof(struct x8664_pda, pcurrent)) \
: "memory", "cc" __EXTRA_CLOBBER)